content: /*
   * Copyright 2017 David Karnok
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package hu.akarnokd.reactive4javaflow.impl.operators;
  
  import hu.akarnokd.reactive4javaflow.*;
  import hu.akarnokd.reactive4javaflow.impl.DeferredScalarSubscription;
  
  import java.util.NoSuchElementException;
  import java.util.concurrent.Flow;
  
  public final class FolyamSingle<T> extends Esetleg<T> {
  
      final Folyam<T> source;
  
      final boolean allowEmpty;
  
      public FolyamSingle(Folyam<T> source, boolean allowEmpty) {
          this.source = source;
          this.allowEmpty = allowEmpty;
      }
  
      @Override
      protected void subscribeActual(FolyamSubscriber<? super T> s) {
          source.subscribe(new SingleSubscriber<>(s, allowEmpty));
      }
  
      static final class SingleSubscriber<T> extends DeferredScalarSubscription<T> implements FolyamSubscriber<T> {
  
          final boolean allowEmpty;
  
          Flow.Subscription upstream;
  
          public SingleSubscriber(FolyamSubscriber<? super T> actual, boolean allowEmpty) {
              super(actual);
              this.allowEmpty = allowEmpty;
          }
  
          @Override
          public void onSubscribe(Flow.Subscription subscription) {
              upstream = subscription;
              actual.onSubscribe(this);
              subscription.request(Long.MAX_VALUE);
          }
  
          @Override
          public void onNext(T item) {
              if (value != null) {
                  value = null;
                  upstream.cancel();
                  error(new IndexOutOfBoundsException("The upstream has more than one item"));
              } else {
                  value = item;
              }
          }
  
          @Override
          public void onError(Throwable throwable) {
              value = null;
              error(throwable);
          }
  
          @Override
          public void onComplete() {
              T v = value;
              value = null;
              if (v == null) {
                  if (allowEmpty) {
                      complete();
                  } else {
                      if (getAcquire() != CANCELLED) {
                          error(new NoSuchElementException("The upstream has no items"));
                      }
                  }
              } else {
                  complete(v);
              }
          }
  
          @Override
          public void cancel() {
              super.cancel();
              upstream.cancel();
          }
      }
  }
  